All Blacks have time to adapt to heat and humidity, says professor

The All Blacks have timed their arrival in Japan perfectly despite a harsh introduction to the country's climate, says an expert in physical performance in stressful conditions.

Images of the All Blacks visibly struggling in the heat and humidity in Japan have filtered back to New Zealand but Jim Cotter, a professor at the school of Physical Education at the University of Otago, reassured New Zealanders that they had given themselves enough time to adapt before their Rugby World Cup opener against South Africa on September 21.

"That's plenty of time," Professor Cotter told Stuff. "They'll have full adaption of what they need by then.

"You don't want it too much more, that's too much time away. That's the time you need.

"Some of them, the slower adapting ones, and there will be slower adapting ones in that unit, they will need the full two weeks, others will be adapted within a week."

The sports science side of the Rugby World Cup is an interesting subplot to the tournament that – at the start at least – will be played in conditions that differ markedly from what most players are used to.

Long-range weather forecasts for Yokohama, where the All Blacks v Springboks game will be held, suggest the clash will be played in temperatures of between 21-26 degrees, with a strong chance of rain.

Those muggy conditions present a challenge for players in all nations, Professor Cotter said.

"Physiologically it costs them," he said. "They're big guys, they generate a lot of heat and they can only store so much heat. We know rugby players even on a cold day get really hot.

"Some of them get to [performance] limiting temperatures so that's going to happen more in Japan.

"It's the humidity in particular. When you generate that much heat you get rid of it, by far the most of it, by evaporation. But humidity limits your ability to get rid of it and limits how much exercise you can do."

Professor Cotter said the British teams would be well supplied with cutting-edge sports science and that "South Africa has fantastic heat research".

Nonetheless, he still saw an opportunity for the All Blacks to use the conditions to their own benefit, by preparing smartly or by picking the right tactical approach to stress their opponents.

"It will affect the play," Professor Cotter said. "It will affect the play of all the teams but by the same token it'll mean there's lot of opportunity to bend it to your favour."

All Blacks coach Steve Hansen has been extolling the virtues of speed and mobility all year, particularly in the front row and loose-forward mix, and on Saturday revealed that some props had lost muscle mass to get them lighter and more agile

Professor Cotter said that strategy was a good fit for Japanese conditions.

"Generally if you are carrying your own body weight, as they do in rugby, the smaller, lighter ones with the biggest surface area relative to their body mass are the ones who do well," he said.

"You don't get any heavy marathoners winning a marathon in a hot, humid climate, or even just a humid climate.

"The team who has those characteristics the most...the All Blacks do pretty well in that regard. Again, that will play into their favour.

"They'll be one of the better teams in that regard."

But, Professor Cotter said, that approach had its own risk profile.

"You just got to hope you don't bleed too many points early on and you make the most of the last 30 minutes," he said.